Ninety percent of post-transfusion hepatitis now appears related to a third human hepatitis "virus" tentatively termed "non-A, non-B". There are several pieces of evidence to suggest this is a virus, but to date this agent has not been observed, has not had a reproducible antigenic marker, has not been grown in culture. This study will attempt to identify bloods with a high probability of containing virus and will inoculate chimpanzees. If chimpanzees are infected, they will be observed for the development of chronic hepatitis, will be reinoculated to stimulate antibody responses, and will be cross challenged to determine if there is more than one non-A, non-B agent.